1. Field of the Invention
The present invention relates to a process for producing hydroxybutyraldehydes by reacting allyl alcohol with carbon monoxide and hydrogen in the presence of a hydroformylation catalyst containing a rhodium component.
2. Description of the Prior Art
Hydroxybutyraldehydes can be easily converted to butanediols by the known hydrogenation.
The typical compound of 1,4-butanediol is one of the important chemical compounds which has various usages such as a starting material for polymers e.g. polyesters, solvents and a starting material for syntheses.
The process for producing butanediol by using hydroxybutyraldehyde has been considered to be advantageous as an industrial process since allyl alcohol which is an economical and easily available petrochemical product.
The process for producing hydroxybutyraldehydes by reacting allyl alcohol with carbon monoxide and hydrogen in the presence of a rhodium complex having an organic tri-substituted phosphine, has been proposed in G.B. Pat. No. 1,493,154; Japanese Unexamined Patent Publication No. 78,809/1977 and U.S. Pat. No. 4,064,145.
This process has advantages in that the reaction condition is mild and the yield is high, etc. However, the process has disadvantages in that the expensive rhodium complex should be used in the process, especially, excess of the expensive organic tri-substituted phosphine should be used as the ligand. Therefore, losses of these compounds should be prevented and the separation, recovery and recycle of these compounds have been significantly important in view of the industrial operation.
The rhodium complex and the organic tri-substituted phosphine respectively have high heat stability and accordingly, it is quite advantageous to employ a distillative separation as the method of separation and recovery of the catalyst.
However, hydroxybutyraldehydes as the main reaction product in the process are thermally unstable. It is well known that hydroxybutyraldehydes are easily converted into high boiling point products by heating them in the presence of the catalyst by the reactions such as an aldol condensation and an acetalation. When the catalyst is separated from said reaction mixture to recycle the catalyst, the high boiling point product is recycled to the reaction system together with the catalyst whereby the high boiling point product is accumulated in the reaction system. It is necessary to have a step of separating the high boiling point product, in order to continue the operation. As a result, the loss or deterioration of the catalyst is sometimes caused. Thus, in the distillative separation with the heating operation, it is the most important to prevent the conversion into the high boiling point product as the reaction product.